Compressed air has many possible fields of application in modern technology. Compressed air is usually produced in a compressed air system from ambient air, which is processed and compressed in the compressed air system. Such processing may comprise especially the drying of the compressed air. One object of drying the compressed air is to reduce the moisture contained in the compressed air, especially to reduce the moisture to a defined residual value. Condensation of this moisture in the compressed air, triggered, for example, by a reduction of temperature and/or pressure, can be avoided thereby.
Air-drying devices, which often have especially an adsorption device, are used for such drying. The air to be dried is sent in such an adsorption device through a desiccant, which is arranged in an adsorption section. Moisture is extracted from the air by the desiccant by adsorption, and the air is dried thereby. Moreover, other components, especially, e.g., carbon dioxide, can also be extracted from the air by suitable desiccants. Thus, drying will hereinafter be defined as both an adsorption of moisture and an adsorption of additional air components, especially carbon dioxide. The adsorption of these air components is especially advantageous in areas in which especially high requirements are imposed on the compressed air provided in terms of composition, especially, e.g., in case of the medical use of compressed air.
The adsorption processes taking place in the desiccant end when the desiccant becomes saturated. Further adsorption of a component of the air being passed through is no longer possible in such case. The adsorbed moisture and the adsorbed air components is/are released again by the desiccant by a regeneration of the desiccant, during which, for example, the desiccant is heated and/or already dry air is introduced through the desiccant. The corresponding adsorption step can then be used again for carrying out a drying operation. Uninterrupted or at least essentially uninterrupted drying of air can be made possible by providing an adsorption device with at least two adsorption steps connected in a fluid-mechanically parallel manner. One of the two adsorption steps is always used to dry the air, while the other is in a regeneration phase or in an inoperative phase.
In prior-art air-drying devices, saturation of the desiccant is usually detected by determining the moisture content in the dried air after passing through the adsorption device or an adsorption section, for example, by dew point measurement. As a result, an adsorption section can be operated until an especially complete saturation of its desiccant with moisture, as a result of which long inoperative phases are obtained for the respective other adsorption section. An especially energy-saving operation of an air-drying device can be achieved hereby. However, this procedure has the drawback that, for example, limit values for other air components may be exceeded, especially already before a saturation of the desiccant with moisture has developed. This may lead to problems especially in relation to carbon dioxide, especially if an air-drying plant is used in the field of medicine.